Fix backgrounds + misc in Island of Moob

- Swapped backgrounds that were using old filepaths and thus did not render
  properly
- Replaced some backgrounds with gradients since there did not seem to
  be viable alternatives to the backgrounds that have been removed
- Expand the first sector of the quiz level to avoid black bars in
  fullscreen at 1080p
- Adjusted the placement of some spawn points in the Tower of Moob level